1. Field of Invention
The present invention relates to a fan. More particularly, the present invention relates to a centrifugal fan.
2. Description of Related Art
In general, a heat-dissipating module is needed in portable electronic devices for the maximum heat-dissipating efficiency. However, because the development of portable electronic devices is toward miniaturization, there are less and less spaces reserved for natural convection within shells of the miniaturized devices. Therefore, the heat-dissipating module for the portable electronic devices has a trend to dissipate heat by forced convection generated from centrifugal fans.
In design of the centrifugal fans, a volute fan shell in the portable electronic devices is introduced to generate high hydrostatic pressure and high rotation speed of air, so as to overcome the issue about poor air convection due to the limited spaces within the shells of the miniaturized devices. However, when the wake flow generated by the blades of the fans hits a surface of a tongue portion, which is the compression section of the shell, the hit region becomes a noise source of narrow band. According to superposition principle, a blade frequency noise will be generated with a large amplitude and a fixed frequency.
In enhancing the heat-dissipating efficiency of the devices, the air amount has to increase as well. However, the increase in the flow field makes the wake flow disturbance by the blades of the fans more intense, resulting in a dilemma between the noise and the heat-dissipating efficiency.